Actuators for actuating a valve mechanism such as a gate valve mechanism, a blow-out preventer or the like may be arranged on the seabed in the maritime gas or oil production. Each valve mechanism comprises a corresponding valve member that, for example, opens or closes a pipe. The valve mechanisms are installed, for example, in a Christmas tree and each valve mechanism is associated with at least one actuator. Such an actuator comprises at least a motor housing with an electric motor and usually a threaded spindle device. By means of the threaded spindle device, rotational motion of the electric motor is transformed into linear motion serving to adjust the respective valve member. For reasons of redundancy, two or more electric motors may be provided, so that in the event of an electric motor failing, the respective task of adjusting the threaded spindle device and thereby the valve member may be assumed by another electric motor.